This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Many functional RNAs fold in the presence of counterions to discrete native structures. A crucial step in this folding process is a global compaction, which has been monitored successfully by small angle x-ray scattering (SAXS) for several RNAs (1-6). For the well-studied Tetrahymena group I ribozyme, this global compaction process occurs with a time constant of ~100 ms, whereas complete folding to the native state is slower by several orders of magnitude due to the formation of at least two misfolded conformations (3, 7, 8). CYT-19 is a DEAD-box ATPase protein that functions in vivo in folding of group I introns and other RNAs. We have recently used ribozyme activity as a readout for native folding to show that CYT-19 accelerates folding from one of these misfolded intermediates by non-specifically promoting partial unfolding (9, 10). This non-specific unfolding allows the more stable native structure to accumulate.